Stereo imaging velocimetry seeks to provide a three-dimensional measurement of the velocity of a fluid. As early as 1973, Elkins et al, in an article titled "Evaluation of Stereoscopic Trace Particle Records of Turbulent Flow Fields," Review of Scientific Instruments, Vol. 48, No. 7, pp. 738-746, (1977) reported an early stereo imaging system using cinematography equipment coupled with an electronic digitizer to track several hundred particles in a turbulent flow. Other early efforts employed a multi-colored approach which allowed higher seeding densities since particles could be separated into groups according to color.
One effort applied this technology to an approved understanding of internal combustion based completely on digital technology., A. A. Adamczyk and L. Ramai, "Reconstruction of a 3-Dimensional Flow Field from Orthogonal Views of Seed Track Video Images," Experiments in Fluids, 6, pp. 380-386, (1988), and "2-Dimensional Particle Tracking (PTV): Technique and Image Processing Algorithms," Experiments in Fluids, Vol. 6, (1988).
Another approach in Canada included performing stereo matching on particles, then tracking the three-dimensional locations in time to reproduce particle motion, R. G. Racca and J. M. Dewey, "A Method for Automatic Particle Tracking in a Three-Dimensional Flow Field," Experiments in Fluids, 6, pp. 25-32, (1988). Most researchers do the opposite, first tracking in two dimensions, then stereo matching the tracks to obtain the third dimension.
Guezennec, et al. have developed a commercially viable instrument that provides qualitative but not quantitative three-dimension results, Y. G. Guezennec, et al. "Algorithms for Fully Automated Three Dimensional Tracking Velocimetry Experiments in Fluids," Experiments in Fluids, 4, (1993).
Raffel, et al. patents, U.S. Pat. No. 5,440,144 and U.S. Pat. No. 5,610,703, disclose a method and an apparatus for measurement of three-dimensional flow velocities. U.S. Pat. No. 5,440,144 relates to a pulsed light method for particle image velocimetry (PIV). When using a pulsed light laser technique, one disadvantage is the complexity of the system while another disadvantage is the small area of the field of view. U.S. Pat. No. 5,610,703 relates to a digital particle image velocimetry (DPIV) method. This patent also describes the use of a pulsed laser light source, but does describe using a CCD camera with a laser source and an electro-mechanical shutter controlled by the DPIV timer box.
U.S. Pat. No. 5,491,642 describes a PIV system which uses pulsed-laser techniques. This patent describes recording the image with a charge coupled device (CCD) camera.
U.S. Pat. No. 4,919,536 describes a system for measuring velocity field fluid flow utilizing a Laser-Doppler spectral image converter, wherein a flow field seeded with small particles is illuminated by a collimated monochromatic sheet of laser light.
The Adrian, et al. Patent, U.S. Pat. No. 4,729,109, describes a method and apparatus for measuring the displacement of particle images through multiple exposure velocimetry with a pulsed laser.
U.S. Pat. No. 5,333,044 discloses a fluorescent image tracking velocimeter that tracks the displacement of fluorescent particles in a fluid over time.
The Cha patent, U.S. Pat. No. 5,532,814, discloses holographic diffraction image velocimetry for three-dimensional, three component particle fields or solid objects.
There are other patents that disclose arrangements which involve the positioning of video cameras at differing angular positions relative to an object such as U.S. Pat. Nos. 5,396,331; 5,110,204; 4,709,580; and 4,337,049. Other laser techniques for determining particle velocimetry are described in U.S. Pat. Nos. 4,988,191 and 5,011,278.
There still exists a need for an apparatus and method that provides state of the art, full-field, three-dimensional flow analysis for any optically transparent fluid seeded with tracer particles regardless of size. Preferably, such a method would not require the use of lasers or other complex equipment with highly specialized optics. Lasers can cause safety concerns as well as limit the type of application. Also, there exists a need for an apparatus and method which would use off-the-shelf hardware that is easily adapted to most three-dimensional applications. It should provide an accuracy to within approximately 2% of full-field which is more accurate than any other three-dimensional system to date. It is desirable to have a modular design with each module being a fully functional stand-alone technique.